When feeding AC power through long cables in transmission systems feeding an electrical load (machines/or other loads), the voltage at consumer end will be heavily influenced by electrical load drawn by the consumer. An example of such a long cable is a cable some kilometers or miles in length connecting a power supply on land to a transformer or to a motor of a pump installed out to sea. In the field of Oil and Gas exploration and production, such loads or machines may be for example be mounted on the seabed tens of kilometers away from land or a topside platform. Electrical equipment such as a subsea multiphase pump or pressure booster pump or a subsea compressor used in Oil and Gas production or transfer installations may be operated underwater, e.g., on the seabed, at depths 1000 meters, or more.
Operating such subsea equipment presents challenges. It is difficult to plan for maintenance of subsea equipment due to an often inaccurate estimate of equipment condition and performance. In the case of a subsea component failure, it is difficult to accurately identify which component has failed. The dynamic performance of the power supply system and loads might change with changing ambient conditions, ageing, various points of operation (frequency, power levels, etc.). It is then difficult for the power supply onshore/platform to be adjusted based on only local measurements, on land or topside. Furthermore, it is difficult to assess capacity limitations of equipment as the information or estimate of the power consumed by the subsea motor is not very accurate, which lack of accuracy normally results in a less optimal planning of production.
The measurement and monitoring of subsea electric machines and the power supplied thereto are critical for the proper functioning of subsea systems where failure of subsea electric machines can be catastrophic. The large distances, remoteness of equipment and difficulties in accessing the subsea electric machines presents unique challenges.